Electromagnetic stirrer arrangement with continuous casting of steel billets and bloom

ABSTRACT

An electromagnetic stirrer arrangement includes a housing having a bottom opening and a top opening. An electromagnetic stirrer is positioned inside the housing. A modular mold assembly includes a mold, a water jacket, a top plate, a bottom plate and a plurality of rods connecting the top and bottom plates. The mold has an open top and an open bottom. The top plate is positioned proximate to the open top of the mold and the bottom plate is positioned proximate to the open bottom of the mold. The connecting rods extend between and securing together the top and bottom plate. The modular mold assembly can easily be replaced by inserting it into or removing from the housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patent application No. 61/238,347 filed on Aug. 31, 2009, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The field is the electromagnetic stirring of continuously cast steel and more particularly to an arrangement of an electromagnetic stirrer and a continuous casting mold assembly.

DESCRIPTION OF THE PRIOR ART

In the production of continuously cast billets and blooms, two types of electromagnetic stirrer (EMS) arrangements with respect to continuous casting mold are commonly used, namely, internal and external.

In the internal EMS arrangement, the stirrer is positioned inside of a mold housing. The stirrer is thus in relatively close proximity to the casting mold the solidifying steel contained therein. With reference now to FIG. 1, a sectional elevation view of an exemplary internal EMS continuous casting mold assembly is shown. The assembly includes a mold 1, water jacket 2, electromagnetic stirrer (EMS) 3, and the mold housing 4. The stirrer 3 is of a rotary type, multi-phase device commonly used for the application for stirring liquid steel (not shown) within the mold 1 during continuous casting operations. The stirrer 3 can be enclosed in a separate housing 5 and is commonly cooled either by water supplied from a closed circuit, or the water used for mold cooling. As seen from FIG. 1, the stirrer 3 is positioned in relatively close proximity to the water jacket 2 and mold 1, which provides the most efficient and effective utilization of the A.C. magnetic field produced by the stirrer 3.

In an external EMS arrangement, the stirrer is installed on the caster within its own enclosure which is arranged around the mold housing. The stirrer internal diameter is sized to accommodate the largest section size of the outside housing of the caster and remains installed on the caster during casting. With reference now to FIG. 2, a sectional elevation view of an exemplary external EMS continuous casting mold assembly is shown. As can be seen, the stirrer 6 is enclosed in the stirrer housing 1 which is installed on a continuous casting machine (not shown). The mold housing 2, which includes the mold 3, water jacket 4, and the foot rolls 5, is inserted inside the inner diameter of the stirrer housing 1 (direction of insertion is indicated by arrow A). Foot rolls are not always required, but are typically necessary for casting practice with increased casting speed and/or larger sections of the casting strand, to provide shell support immediately below the mold.

In order to accommodate the mold housing 2 and the attached foot rolls 5, the internal diameter of stirrer housing 1 should be substantially large in comparison with that of the stirrer 3 arranged internally within the mold housing 4, as shown in FIG. 1.

Though the above described molding assemblies have proven to be adequate, drawbacks persist. Thus, there is a need in the art for a new continuous casting arrangement with EMS.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an electromagnetic stirrer arrangement is disclosed. The electromagnetic stirrer arrangement includes a housing having a bottom opening and a top opening. An electromagnetic stirrer is positioned inside the housing. A modular mold assembly includes a mold, a top plate, a bottom plate and a plurality of rods connecting the top and the bottom plates. The mold has open top and bottom ends. The top plate is positioned proximate to the open top end of the mold and the bottom plate is positioned proximate to the open bottom end of the mold. The connecting rods extend between and securing together the top and bottom plate. The modular mold assembly is designed to allow replacement of a mold (insertion into or removal from) in the housing.

According to another aspect of the present invention, an electromagnetic stirrer arrangement is disclosed. The electromagnetic stirrer arrangement includes a housing having a bottom opening and a top opening. An electromagnetic stirrer is positioned inside the housing. A modular mold assembly includes a mold, a top plate, a bottom plate and a water jacket. The mold has open top and bottom ends. The top plate is positioned proximate the open top of the mold and the bottom plate is positioned proximate the open bottom of the mold. The water jacket is positioned around the mold to form a channel therebetween for directing cooling fluid over an exterior surface of the mold. The modular mold assembly is insertable and removable from the housing.

DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional elevation view of a prior art internal EMS arrangement in a continuous caster mold housing assembly.

FIG. 2 is a sectional elevation view of a prior art external EMS arrangement with the continuous caster mold housing assembly.

FIG. 3 is a graph showing the effect of stirrer internal diameter (ID) on magnetic flux density at a constant kVA input.

FIG. 4 is a graph showing the effect of stirrer ID on stirring velocity within the casting mold.

FIG. 5 is a graph showing the effect of stirrer ID on the kVA input required to maintain a constant level of magnetic flux density.

FIG. 6 is a sectional elevation of a hybrid EMS arrangement in a continuous caster mold housing assembly.

FIG. 7 is a sectional elevation of the casting mold modular assembly.

DETAILED DESCRIPTION

The internal diameter of an electromagnetic stirrer (EMS) affects the magnetic flux density value in a continuous casting mold. In turn, this affects stirring velocity in the melt induced by the magnetic field created by the EMS. At a constant apparent power input to the EMS (in kVA), magnetic flux density declines as the EMS internal diameter increases. This phenomenon is shown in the graph of FIG. 3. For illustrative purposes, the curve indicates values of flux density between the typical diameter of an internal EMS, and external EMS without a foot roll attached to the mold housing assembly and an external EMS with a foot roll attached to the mold housing assembly of the same section size mold.

As seen from FIG. 3, EMS diameter has a marked effect on magnetic flux density when power input and operating frequency are held constant. The intensity of stirring in the melt is one of the main defining factors of EMS metallurgical performance and quantitatively, stirring intensity is commonly determined by melt stirring velocity.

With reference now to FIG. 4, the effect of EMS internal diameter on stirring velocity is shown, where the power input (kVA) and operating frequency are held constant. For clarity, the same input values are used in FIG. 4 as those in FIG. 3. Similar to the effect on magnetic flux density, the effect of stirrer internal diameter on stirring velocity is very strong. The marks on the curve shown in FIG. 4 while not identified in that figure are for the same types of stirrer arrangements as the corresponding marks shown in FIG. 3.

The effect of an EMS internal diameter increase on the decline of magnetic flux density and stirring velocity may be counteracted by increasing power input to the EMS. However, due to practical limitations, this requirement often cannot be fulfilled, as the required power input is exponentially related to EMS internal diameter, as illustrated by FIG. 5.

With reference now to FIG. 6, a sectional elevation of a continuous casting arrangement is shown and generally indicated by the numeral 100. FIG. 7 shows a sectional elevation of a casting mold modular assembly 120 removed from the casting arrangement 100. It should be appreciated that like reference numerals are used to identify like elements in both FIG. 6 and FIG. 7. The casting arrangement 100 can be used with any continuous casting molds, i.e. vertical or curved type, employed for the production of steel billets and blooms of different cross-section sizes and geometry. The casting arrangement 100 includes an exterior mold housing 101 which surrounds a casting mold 102 when the casting mold modular assembly 120 is installed. Housing 101 is open at the top and bottom so that it can receive casting mold modular assembly 120. An electromagnetic stirrer (EMS) 105 is arranged within mold housing 101 and it may also be cooled by the same mold cooling water or by water supplied through a designated cooling system. If a designated cooling system is employed, specially prepared cooling water may be used to cool EMS 105. In such an instance, a separator 106 may be positioned within housing 101 and interior to EMS 105 to keep separate the mold cooling water from the EMS coolant. The EMS 105 is a multi-phase electrical device similar to the stator of an asynchronous motor which is comprised of an iron-made stator that has mounted on it electrical windings. The EMS 105 operates at a low frequency A.C. current, typically within the range of 2 to 8 Hz, producing a rotating A.C. magnetic field which sets up the stirring motion of the melt (not shown) within the mold 102.

The modular assembly 120 includes the casting mold 102 which is fabricated from a copper alloy and has an open end on each side for delivery of liquid steel through the top opening T and withdrawal of the cast strand with solidifying core (not shown) through the bottom opening B. A water jacket 103 surrounds the mold 102 and forms a channel 104 between the outer surface of mold 102 and the inner surface of water jacket 103. Cooling water is directed through channel 104 to cool the mold 102.

The casting mold modular assembly 120 shown in FIG. 7 further includes an upper plate 107 and a lower plate 108 that are positioned proximate to the top T and bottom B opening of mold 102. Plates 107 and 108 include a central opening 121 and 122 respectively (see FIG. 6), that is generally sized to receive mold 102 therein. Plates 107 and 108 are rigidly attached together by a plurality of rods 109 that extend parallel to and are spaced from mold 102. According to one embodiment, at least four (4) rods 109 extend between top and bottom plates 107 and 108 in an evenly spaced arrangement. According to another embodiment eight (8) rods extend between top and bottom plates 107 and 108 in an evenly spaced arrangement. Each rod 109 may be secured to the respective plate 107 and 108 with screws 110. In this manner, a rigid, modular, cage-like structure is formed.

As shown in FIG. 6, top plate 107 includes a groove 112 on central opening 121 and bottom plate 108 includes a groove 111 on central opening 122. Grooves 111 and 112 are adapted to receive o-rings 123 that provide a water tight seal between the mold 102 and the plates 107 and 108. Bottom plate 108 further includes a second groove 125 on the outer facing surface thereof. Groove 125 is adapted to receive an o-ring 126 that provides a water tight seal between plate 108 and housing 101.

A plate 116 extends outwardly from the top end of water jacket 103, circumferentially around mold 102. Plate 116 segments the interior of housing 101 to prevent mixture of incoming and outgoing cooling water flows (water flows represented by arrows). Upper plate 107 supports mold 102 by preventing axial displacement. Further supporting mold 102 is a plate 117 positioned below and flush with top plate 107. Plate 117 is coupled to the plate 107, surrounds mold 102 and is received in a groove 125 on the outer surface of mold 102. A protecting plate 113 of the mold housing 101 includes an opening substantially the same size as mold 102 and is secured to top plate 107. Protecting plate 113 protects top plate 107 from damage in event of liquid steel spillage.

With reference now to FIG. 7, it can be seen that modular assembly 120 can be easily removed from the mold housing 101 and replaced. This is achieved by releasing the bolts 114 (see FIG. 6) securing the upper plate 107 of modular assembly 120 to a flange 115 of mold housing 101.

It should be appreciated that the casting arrangement 100 described herein includes the features and advantages found in both internal and external EMS arrangements. Specifically, the “hybrid” arrangement provides the benefits of an internal EMS arrangement in terms of energy efficiency and metallurgical effectiveness while also enabling convenient and speedy casting mold changes, similar to an external EMS arrangement.

It should further be appreciated that, compared to an internal EMS arrangement, the casting arrangement 100 minimizes capital costs of equipment installation by reducing the number of mold housings and stirrers when the used with a multiple strand section caster. Further, operating costs are reduced compared to external EMS due to the smaller relative internal diameter of the EMS. Smaller internal diameter leads to reduced power requirements to attain operating values of magnetic flux density and frequency. Operating costs savings become especially significant when cast strand section sizes are within a wide range, e.g. 100 mm sq. to 200 mm sq. or greater.

It should also be appreciated that modular mold assembly 120 is configured to be fixed within the mold housing with mold section sizes based on stirrer design and operating parameters in order to assure maximal stirring effectiveness.

It should also be further appreciated that the casting arrangement 100, allows for convenient and relatively rapid replacement of casting mold 102 in accordance with the production schedule of casting operations by using the removable modular assembly 120. This assembly does not include the mold housing 101 and EMS 105 as they are common to the existing mold housing assemblies. Each mold modular assembly 120 can be exchanged for another one, if required, within the mold housing 101 equipped with the EMS 105.

The replacement procedure takes place at a mold preparation shop, in accordance with production schedule requirements. The amount of time and labor required for replacement of the modular mold assembly 120 is markedly reduced in comparison with that required for changing a mold in a typical internal EMS arrangement. Further, in applications with a multiple section size caster, the amount of mold housings to be used with the modular mold assembly is also drastically reduced in comparison with that required for prior art internal and external EMS arrangements. These advantages, combined with greatly reduced operating costs over the external EMS arrangement, result in substantial economic benefits in comparison with the existing conventional EMS arrangements.

It is to be understood that the description of the foregoing exemplary embodiment(s) is (are) intended to be only illustrative, rather than exhaustive, of the present invention. Those of ordinary skill will be able to make certain additions, deletions, and/or modifications to the embodiment(s) of the disclosed subject matter without departing from the spirit of the invention or its scope, as defined by the appended claims. 

1. An electromagnetic stirrer arrangement comprising: a housing having a bottom opening and a top opening; an electromagnetic stirrer positioned inside said housing; a modular mold assembly including a mold, a top plate, a bottom plate and a plurality of connecting rods, said mold having an open top and an open bottom, said top plate being positioned proximate said open top of said mold and said bottom plate positioned proximate said open bottom of said mold, said rods extending between and securing together said top and bottom plate; and wherein said modular mold assembly is insertable and removable from said housing.
 2. The electromagnetic stirrer arrangement of claim 1 wherein said plurality of connecting rods comprises four (4) rods positioned in an evenly spaced arrangement around said mold.
 3. The electromagnetic stirrer arrangement of claim 1 wherein said plurality of connecting rods comprises eight (8) rods positioned in an evenly spaced arrangement around said mold.
 4. The electromagnetic stirrer arrangement of claim 1 wherein said modular mold assembly further comprises a water jacket positioned between said plurality of connecting rods and said mold for directing cooling fluid over an exterior surface of said mold.
 5. The electromagnetic stirrer arrangement of claim 1 wherein said bottom plate includes a central opening and said top plate includes a central opening, said mold being positioned within each said central opening.
 6. The electromagnetic stirrer arrangement of claim 1 wherein said bottom plate central opening and said top plate central opening each include a groove and receives an o-ring therein, said o-ring engaging said central opening and an exterior surface of said mold.
 7. The electromagnetic stirrer arrangement of claim 1 wherein said electromagnetic stirrer is supplied with an A.C. current at a frequency of 1 to 10 Hz and intensity between 50 and 550 Amps.
 8. The electromagnetic stirrer arrangement of claim 1 wherein said housing extends between said top plate and said bottom plate to encapsulate said mold.
 9. An electromagnetic stirrer arrangement comprising: a housing having a bottom opening and a top opening; an electromagnetic stirrer positioned inside said housing; a modular mold assembly including a mold, a top plate, a bottom plate and a water jacket, said mold having an open top and an open bottom, said top plate being positioned proximate said open top of said mold and said bottom plate positioned proximate said open bottom of said mold, said water jacket positioned around said mold to form a channel therebetween for directing cooling fluid over an exterior surface of said mold; and wherein said modular mold assembly is insertable and removable from said housing.
 10. The electromagnetic stirrer arrangement according to claim 9 further comprising a plurality of connecting rods extending between and securing together said top and bottom plate.
 11. The electromagnetic stirrer arrangement according to claim 10 wherein said plurality of connecting rods comprises four (4) rods positioned in an evenly spaced arrangement around said mold.
 12. The electromagnetic stirrer arrangement according to claim 10 wherein said plurality of connecting rods comprises eight (8) rods positioned in an evenly spaced arrangement around said mold.
 13. The electromagnetic stirrer arrangement of claim 9 wherein said bottom plate includes a central opening and said top plate includes a central opening, said mold being positioned within each said central opening.
 14. The electromagnetic stirrer arrangement of claim 10 wherein said bottom plate central opening and said top plate central opening each include a groove and receives an o-ring therein, said o-ring engaging said central opening and an exterior surface of said mold.
 15. The electromagnetic stirrer arrangement of claim 11 wherein said electromagnetic stirrer is supplied with an A.C. current at a frequency of 1 to 10 Hz and intensity between 50 and 550 Amps.
 16. The electromagnetic stirrer arrangement of claim 9 wherein said housing extends between said top plate and said bottom plate to encapsulate said mold. 